Ozy Clint,
I just went through this process this year and had real good results... I really like the Beman MFX Classics. I was given 4 used 400s & 8 or 9 340s so I worked up two solutions I could use interchangeably depending on broadhead choice. I too found STU's calculator to be pretty accurate BUT you absolutely need to enter the data correctly for the inserts & footing info, then you're golden.... The insert weight does not impact as directly as you might think when you go to the 100grains because they're pretty long which shortens the dynamic shaft portion. I don't have time to elaborate right now but I've included a thread link to a very successful season using these! I'd be happy to dialogue and send you a copy of the STU calculator spreadsheet forms already configured so you can tweak and analyze...!??
http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=1;t=123089 Setup#1
Beman MFX 400, 29", 50 grain brass insert, 1.125"aluminum footing
(3) 5" Right Wing Helical Fletch, 7" Black Widow Wrap + Clear Wrap
175 Grain VPA Terminator 3- Blade Broadheads
Setup #2
Beman MFX Classic 340, 29", 1.125" Aluminum footing, standard 16 grain aluminum hidden insert
(3) 5" Right wing helical fletching, 7" Black Widow Wrap + clear wrap
Abowyer Right Wing Single Bevel 260 or 270 grain broadheads
Black Widow KB
53lbs @28", I draw 27.5"